1. Field of the Invention
The invention concerns a method according to the preamble of claim 1 and a safety device according to the preamble of claim 9.
2. Description of the Related Art
There is a known method for the remote control of self-propelling working machines, especially soil-compacting machines such as rollers, vibration plates or the like, in which control signals are sent by means of a transmitting unit, which can be operated by an operator and are separate from the working machine, to a receiving unit on the working machine and are processed by the receiving unit for generating an electrical control signal for controlling the working machine.
In the remote control of self-propelling working machines it must be ensured that an adequate safety distance is maintained between the operator and the working machine to rule out any danger to the operator from the running working machine. In the case of trench rollers there are legal regulations prescribing a minimum distance between the trench roller and the operator. If the distance is not respected, all potentially dangerous movements must be prevented, so that the trench roller must be immediately stopped.
DE 42 21 793 C1 discloses an infrared remote control for self-propelling soil-compacting machines which sends from a control device carried by the operator not only the infrared control radiation intended for the functional control of the working machine but also infrared near-range radiation at much lower intensity than the control radiation, so that this near-range radiation can be received with adequate intensity only in close proximity to the transmitter. When this near-range radiation is received, the generation of electric signals, which are caused by the control radiation and otherwise make the working machine move along, is suppressed in the receiving unit on the working machine.
Using this method, the working machine can be moved as long as a safety signal does not arrive with adequate intensity at the working machine. Attenuations of the signal intensity that are not based on a large distance between the transmitter and receiver required for safety reasons may lead to the working machine still being able to move even if the safety distance is no longer being respected. Such a source of error results from the fact that the receiving eye, for example on a trench roller, is usually not arranged centrally, with respect to the direction of propulsion, but at the intended place for the operator in the region of one of the end faces. This produces an unsymmetrical receiving field with respect to the trench roller, with the effect that, when the operator with the transmitter is in front of the end face of the machine away from the receiving eye, the actual safety distance between the operator and the machine is shortened by the distance which exists between this end face and the receiving eye, that is for example by 2 m in comparison with the safety distance when the operator is in front of the other end face of the machine. If the operator stands very close to the end face of the machine away from the receiving eye, this effect is intensified even further by the fact that the assumed 2 m of machine length that have to be bridged between the transmitter and the receiving eye can shield the radiation. While the weak safety signals cannot reach the receiving eye for the reasons mentioned, the strong control signals, which may be reflected by lateral trench walls, arrive at the receiving eye and, as a result, give the impression that there is an adequate safety distance.
If the receiving eye for the safety signal is located on the working machine, there is a tendency for it to become soiled, which may cause signal attenuation. This may also have the effect of giving the false impression of an adequate safety distance, even if the predetermined safety distance is no longer being respected.
DE 196 00 791 A1 discloses a remote control in which the distance of the remote control devices from a working machine is concluded from the signals sent by evaluating the phase or intensity of the signals, in order to avoid the overlapping of effective ranges of different remote controls. The purpose of this arrangement is to limit as accurately as possible the range of each radio control transmitter to a fixed working range, in order to avoid any danger to personnel in the working and effective range of the radio-remote-controlled equipment.